Method for laser cutting tubing using inert gas and a disposable mask

ABSTRACT

A method for making a device includes providing a tubular member which will be formed into the device, masking at least a portion of the inner surface of the tubular member with a removable sacrificial material, selectively removing a portion of the tubular member and sacrificial material using a laser device, and mechanically removing the sacrificial material from the inner surface of the tubular member. The method may also include applying a chemical solution to the tubular member and sacrificial material which primarily attacks the either the tubular member or sacrificial material.

BACKGROUND OF THE INVENTION

The present invention relates generally to methods for laser cutting ahollow workpiece, such as a length of tubing. The present invention ismore particularly directed to methods for fabricating medical devices,such as, for example, expandable endoprostheses, commonly known asstents, using a sacrificial masking material which helps to preventdamage to the workpiece when cutting the workpiece with a laserapparatus that utilizes an inert gas, instead of air or oxygen, in thecutting process.

Stents are particularly useful in the treatment and repair of bloodvessels after a stenosis has been compressed by percutaneoustransluminal coronary angioplasty (PTCA), percutaneous transluminalangioplasty (PTA), or removed by atherectomy or other means, to helpimprove the outcome of the procedure and reduce the possibility ofrestenosis.

Stents are generally cylindrically shaped devices which function to holdopen, and sometimes expand, a segment of a blood vessel or otherarterial lumen, such as a coronary artery. Stents are usually deliveredin a compressed condition to the target site and then deployed at thatlocation into an expanded condition to support the vessel and helpmaintain it in an open position.

Prior art stents typically fall into two general categories ofconstruction. The first type of stent is expandable upon application ofa controlled force, often through the inflation of the balloon portionof a dilatation catheter which, upon inflation of the balloon or otherexpansion means, expands the compressed stent to a larger diameter to beleft in place within the artery at the target site. The second type ofstent is a self expanding stent formed from shape memory metals or superelastic nickel titanium alloys (Nitinol), which will automaticallyexpand from a compressed state when the stent is advanced out of thedistal end of the delivery catheter into the blood vessel.

Stents can be formed with strut patterns which when expanded have alarge amount of open space, but when collapsed have little space betweenthe often tortuously shaped struts forming the stent. One method ofmaking a stent includes laser cutting a tubular member or tubing ofsuitable material to create the intricate strut patterns which definethe structure of the stent. Laser cutting generally provides a precisemethod for forming these intricate strut patterns in the tubing used toform the stent. Such patterns require the tubing to be cut through oneside of the wall of the tubing without cutting through the opposite sideof the tubing.

In the past, laser apparatus utilizing pressured air (oxygen) have beenused to cut the tubing. Generally, a laser beam locally heats the tubingmaterial while pressurized air is blown through a small coaxial orificedirectly onto the heated region in order to create a slot or “kerf”through the wall of the tubing.

Laser cutting of a length of tubing generally begins by focusing a laserbeam on a targeted spot on the tubing. The spot is melted and ispreferably vaporized, or at least partially vaporized, by the laserbeam. Once the laser beam burns through the side wall of the tubing, thebeam will usually continue to strike the opposite side wall of thetubing, and may begin to vaporize, or partially vaporize, the oppositeside wall of the tubing. This undesirable burning or partialvaporization of the opposite sidewall is called “burn through” and canresult in the weakening of opposite sidewall. In some cases, burnthrough may result in the workpiece being discarded. The melting andvaporization of the tubing also can form “recast” material, which ismaterial from the tubing that has melted and resolidified on laser-cutsurfaces. The recast material, also referred to as “dross,” may includemetal oxides and impurities which are undesirable in the manufacturingprocess since the recast material must be thoroughly removed from thesurface of the stent. Oxidation can make a stent more susceptible tofailure (e.g., cracking or fracture) during manufacturing or, if notcompletely removed, in use. Additionally, recast material can beparticularly difficult to remove without damaging the thin strutscreated by the laser cutting operation. Therefore, both burn through andformation of recast material presents a formidable problem to the stentmanufacturer.

The problems of laser cutting self-expanding stents made from a materialsuch as Nitinol are further enhanced when pressurized air or oxygen isused to create the cut pattern. Because Nitinol is composed of about 50%titanium, a notoriously reactive metal, the titanium readily reacts withthe oxygen in the air when heated. As a result, the material expelledduring the cutting procedure is predominately comprised of metal oxides,most of which are trapped inside the tubing and adhere to the metallicinner surface of the Nitinol tube. Side walls of the slot or kerf alsobecome oxidized during the cutting process, making the as-cut stent lessductile and thereby more susceptible to cracking or complete fractureduring radial expansion or during other subsequent manufacturing steps.As a result, a laser cut Nitinol work piece must be carefully processedby a number of different cycles of chemical treatment, radial expansion,and heat stabilization to achieve the final stent size.

Any remaining oxidized wall material and other adhered oxide debris mustfirst be removed in order to attain an acceptably smooth surface laterduring electropolishing. This additional clean up procedure can beachieved through a combination of automated grit blasting, manual gritblasting and chemical removal of oxide prior to electropolishing. Somemethods require the physical removal of the recast material using areamer or similar equipment and can often damage the thin struts of thestent. While electropolishing procedures can remove some recastmaterial, often the recast material may be so heavily clad on thesurface of the stent that not all of the recast material can be removedby this process. Additionally, the electropolishing process will removematerial from the struts so it is important that only a small amount ofthe strut surface is actually removed. For example, if theelectropolishing procedure is too long in duration, due to accumulatedrecast material, portions forming the struts of the stent may have toomuch material removed, resulting in a damaged or generally weakenedstent.

Certain methods have developed to deal with the problem caused by burnthrough and the formation of recast material on the workpiece. One suchmethod uses a continuous metal wire run through the tubular workpiece tocreate a “protective barrier” which somewhat helps to prevent the laserbeam from striking the opposite sidewall of the tubing. Another systemutilizes a liquid flushed through the workpiece as it is being cut. Thefluid is usually fed through one end of the tubing and exits through theopposite end of the tubing, along with the newly formed openings in thewall of the tubing created by the laser. The liquid flushes away some ofthe recast material being created by the vaporization of the tubing.However, the presence of this liquid does not always completely blockthe laser beam, which can allow the inside wall of the tubing to beheated and damaged. Additionally, the use of liquid requires additionalequipment for handling the liquid including discharge equipment, catchbasins, waste disposal, and other processing equipment.

It has been anticipated that Nitinol stents could be laser cut using aninert gas such as argon or helium to prevent sidewall oxidation whichwould help prevent cracking or fracturing during subsequent processing.The absence of oxygen in the cutting process also will help to preventthe recast material from being oxidized. However, laser cutting Nitinoltubing utilizing pressurized argon gas typically cannot directly producea finished stent because the expelled melted material formed during thecutting process can become “welded” to the inner wall of the tubing.This welded metallic build up could possibly be removed by laterprocessing including reaming, drilling, electric discharge machining andthe like but with difficulty and risk to the integrity of the workpiece.

What have been needed and heretofore unavailable are improved methodsfor reducing the adverse results caused by burn through along with theelimination of oxidation during the laser cutting process. The presentinventions disclosed herein satisfy these and other needs.

SUMMARY OF THE INVENTION

The present invention is directed to methods for laser cutting a tubularworkpiece which helps to reduce the number of post-cutting processingsteps by preventing oxidation and preventing recast from adhering to theworkpiece material during the laser cutting process. The presentinvention prevents oxidation of the workpiece by utilizing a laserapparatus that utilizes an inert gas, such as argon or helium, ratherthan air or oxygen, to create the slots or kerfs which form the patterncut into the workpiece. The absence of oxygen in the cutting processthus prevents the workpiece from being oxidized during laser cutting.The present invention also utilizes a disposable, sacrificial mask whichhelps to prevent damage to the workpiece by covering the surface of theworkpiece as it is being laser cut. The present invention isparticularly beneficial in manufacturing intricately shaped devices froma hollow workpiece, such as a stent.

In one aspect of the invention, the disposable mask can be placed overat least a portion of the inner surface of the tubular member or tubingwhich is being laser cut. In the laser cutting process, recast materialformed during the cutting process is forced through the kerf via thepressurized inert gas and is collected on the surface of the disposablemask, rather than on the inner surface of the tubular member. Tubingmade from Nitinol can be laser cut using an inert gas without the riskof the recast material being welded onto the inner surface of thetubular member. During the cutting operation, both the tubular memberand the disposable mask are simultaneously cut to the same pattern.During cutting, the expelled molten Nitinol collects on the innersurface of the disposable mask instead of directly on the inner surfaceof the tubular member, and afterward the expelled material andsacrificial mask can be removed because neither are strongly affixed tothe inner surface of the Nitinol workpiece. Because the inert gasprevents oxidation of the sidewalls of the tubular member, the presentinvention allows the cut workpiece to be further processed with littleor no need to grit blast tough oxidized material from the stent wallprior to electropolishing.

After the tubular member and sacrificial mask have been laser cut, therewill be a build up of recast material formed along the bottom edges ofthe kerfs and elsewhere along the workpiece. Expelled molten materialfrom the tubular member will collect on the inner surface of thesacrificial mask rather than being directly welded on to the innersurface of the tubular member. However, the recast material must stillbe removed from the laser-cut tubular member prior to electropolishing.

The present invention utilizes a variety of mechanical techniques toremove the sacrificial mask from the tubular member, along with avariety of chemical removal techniques which can be coupled with themechanical techniques to quickly and cleanly remove the dross andsacrificial mask from the inner wall of the formed tubular member.

In one particular aspect of the present invention, the purely mechanicaltechniques for removing the dross and sacrificial mask is to attack thedross only, utilizing equipment which will grind, hone or bead-blast thedross only. Dross also can be removed utilizing a tool such as a wirebrush or reamer. Another way to clean the lased tubular member would beto mechanically attack the sacrificial mask only. Similar mechanicaltechniques could be used to remove the sacrificial mask. Lastly, thesesame techniques could be used to mechanically attack both the dross andsacrificial mask. These various techniques provide simple but usefulmanufacturing steps to separate the lased tubular member from thesacrificial mask and dross.

In other aspects of the present invention, mechanical techniques toseparate the components include employing different material propertiesbetween the lased tubular member and the sacrificial mask. For example,the tubular member and sacrificial mask could be made from differentmaterials having different coefficients of thermal expansion.Application of heat or cold to the tubular member and sacrificial maskcould then be used to break the sacrificial mask away from the lasedtubular member.

In another mechanical procedure, a lased tubular member made from aself-expanding material, such as Nitinol, could be crushed and rolled toallow the tubular member to spring back to shape. Since the sacrificialmask is not superelastic, the crushing and rolling of the tubular membershould break any connection between the sacrificial mask and the tubularmember. Alternatively, the lased tubular member could be expanded,rather than being rolled, thereby causing the sacrificial mask to breakaway from the tubular member.

Still other removal procedures which can be implemented in accordancewith the present invention include mechanically peeling the sacrificialmask from the lased tubular member or mechanically gripping andpulling/pushing the sacrificial mask out of the tubular member. Removalprocedures could alternatively call for the tubular member/sacrificialmask to subjected to vibration, which would break the sacrificial maskfrom the tubular member.

In another aspect of the present invention, the procedure for removingthe sacrificial mask and dross from the lased tubular member wouldutilize a combination of chemical removal techniques with mechanicalremoval techniques, such as the ones addressed above. For example, aftercutting, the lased tubular member and sacrificial mask can be subjectedto a chemical attack which would only attack the tubular member materialtherefore dissolving the dross. A chemical solution would be applied toboth the tubular member and sacrificial mask. The application of thechemical solution is designed to primarily attack the tubular member,rather than the disposable mask material. As such, the chemicals areselected which preferably attack the material of the tubular member,leaving the sacrificial mask material generally unharmed. In one aspectof the invention, the chemical solution attacks the tubular member byetching it. It should be noted that the recast material (especially thethin connection between the sidewall and recast metal) has a very largesurface area to volume ratio and therefore it is much more readilyattacked by the chemical solution than the body of the tubular memberitself. This process of applying a chemical solution which primarilyattacks the material forming the tubular member eliminates or weakensmuch of the recast material formed in the kerfs and elsewhere, therebyallowing the tubular member and the sacrificial mask material to be moreeasily separated.

After the chemical solution has acted on the tubular member, the tubularmember and the sacrificial mask material are mechanically separated.This mechanical separation causes any recast material that is stilladhering to the tubular member to be broken off, leaving the innersurface of the tubular member virtually free of any recast material. Theremoval of the sacrificial material from the inner surface of thetubular member can be performed mechanically, for example, by deviceswhich will break the recast material formed in the kerfs and elsewhere.The mechanical process of removing the sacrificial material from thetubular member can be performed, for example, by inserting a mandrelinto the inner lumen of the disposable mask and twisting the sacrificialmask from the inner surface of the tubular member. Any of the mechanicaltechniques mentioned above could be implemented to remove thesacrificial mask and any remaining dross from the tubular member.

In another aspect of the present invention, the removal process wouldencompass the application of a chemical solution which attacks only thesacrificial mask, leaving the tubular member virtually unharmed. Thechemical attack can either dissolve the sacrificial mask completely, orcould just weaken the sacrificial mask. Any one of a number ofmechanical procedures could then be implemented to remove any remainingportions of the sacrificial mask and dross.

The removal process could encompass the application of chemicals whichattacks both the sacrificial mask and tubular member. In this aspect ofthe invention, a chemical solution could first be applied which attacksor dissolves only the dross, then a second chemical solution could beapplied which attacks only the sacrificial mask. Alternatively, thechemical solution which only attacks the sacrificial mask could beapplied first and later the chemical solution which attacks the drosscould be applied. In yet another removal procedure, a chemical solutionwhich simultaneously attacks both the tubular member and sacrificialmask could be applied. In one scenario, the chemical solution couldcompletely dissolve the sacrificial mask and dross. Alternatively, ifthe solution only weakens the dross and sacrificial mask, any remainingdross and mask material could be mechanically removed using any of themechanical techniques mentioned above.

In another aspect of the invention, the disposable mask can take theshape of a tubular sleeve that is placed snugly against the insidesurface of the tubular member. The disposable mask preferably assumesthe form of a thin wall tube whose outer diameter closely matches theinner diameter of the tubular member. Alternatively, the mask may becomprised of a flat foil that is rolled into a cylinder and theninserted into the tubular member. In other aspects, the disposable maskmay be produced through the build-up of material such as byelectroplating, plasma spray, physical vapor deposition, chemical vapordeposition and the like. However, the disposable mask material shouldnot become metallurgically bonded or otherwise so strongly affixed tothe tubular member that the two components cannot be easily separatedfrom each other after laser cutting. Additionally, the disposable maskand the work piece should be made from dissimilar materials that do noteasily weld or bond to one another.

In another particular aspect of the present invention, steel orstainless steel is used to form the disposable mask when the workpieceis being formed from binary nickel-titanium or a nickel-titanium alloydue to the inherent metallurgical incompatibility of these materials.The disposable mask also could be made from any suitable materialcapable of withstanding the temperatures of the expelled molten Nitinolmaterial, for example, ceramics, metals, composites, or high temperaturepolymers.

The pressurized inert gas used with the laser apparatus could be argonor helium as these two inert gases are economical and commerciallyavailable. However, it should be understood that the laser cutting ofthe tubular metallic work piece could utilize any inert or nonreactive,oxygen-free gas to prevent oxidation during the cutting process.

The use of the present method in forming a medical device, such as astent, eliminates the need for grit blasting or otherwise chemicallyremoving the oxidized cast material prior to electropolishing since airor oxygen is no longer used in the laser cutting process. The use of theinert gas eliminates the possibility that the sidewalls of the tubularmember and recast material will become oxidized during laser cutting. Asa result, the elimination of sidewall oxidation helps to preventcracking or fracturing of the stent during use and eliminates some ofthe subsequent processing which would be otherwise be needed to removethe oxidized material from the tubular member. As a result, the formedworkpiece can be sent for electropolishing without the need foradditional processing which could break or irreparably damage thefragile struts which form the stent.

These and other advantages of the present invention become more apparentfrom the following detailed description of the invention, when taken inconjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a schematic of a method of making adevice, such as a stent, from a tubular member using a laser devicewhich uses an inert gas to assist in the cutting process;

FIG. 2 is an end view showing the resulting formation of recast materialon the inside surface of a tubular member when the laser cuts one sideof the tubular member;

FIG. 3 is schematic side view showing the laser cutting of the tubularmember mounted on a disposable sacrificial mask;

FIG. 4 is a side elevational view showing the resulting build up ofrecast material or “slag” along the bottom edge of the slot or kerfformed on the tubular member which must be removed prior toelectropolishing; and

FIG. 5 is a side elevational view showing the disposable mask and recastmaterial removed from the inner surface of the tubular member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawing in which reference numerals represent likeor corresponding elements across the drawings, and particularly FIGS. 1and 3-5, a method of making a device from a hollow tubular member 10 isgenerally disclosed. The present invention relates generally to methodsfor laser cutting a length of hollow tubing, or as is it referred toherein a “tubular member,” to form a device, typically a medical device,such as a stent. While most workpieces formed in accordance with thepresent invention are in the form of a tubular member having a circularcross section, the tubular member could have a non-circular crosssection as well. For example, the tubular member could have arectangular, oval, square, and the like cross section, if desired.Moreover, the invention is not limited to forming stents and has a wideapplication with respect to other laser cut medical devices andnon-medical products, particularly products which require a highprecision pattern that is cut utilizing a laser cutting process.

Referring specifically to FIG. 1, in one particular form of the presentinvention, the method includes providing a tubular member 10 which willbe formed into the finished device. The tubular member 10 has an outersurface 12 along with an inner surface 14. The tubular member 10 is madefrom a particular material suitable for the finished device and is to belaser cut, as will be described herein, to generally form the desiredpattern and shape of the finished workpiece. The present invention isparticularly useful in cutting a tubular member made from anickel-titanium alloy (Nitinol) or a ternary nickel-titanium alloy suchas nickel-titanium-platinum. When a stent is being fabricated, thetubular member will be laser cut to remove portions of the tubularmember to create the desired strut patterns of the stent. It should beappreciated that additional processing of the workpiece may be neededafter initial laser cutting to achieve the final finished product.

As can be seen in FIG. 1, the tubular member 10 is shown in contact witha disposable mask made from a sacrificial material that will besimultaneously laser cut with the tubular member 10, but will be laterremoved in subsequent processing. This disposable mask, shown in thisparticular embodiment of the invention as a masking sleeve 16, is placedwithin the tubular member 10 to cover or mask at least a portion of theinner surface 14 of the tubular member 10. This masking sleeve 16includes an outer surface 18 and an inner surface 20. The masking sleeve16 is placed snugly against the inside surface 14 of the tubular memberand can be later removed from contact with the tubular member 10. Thedisposable mask can be formed as a thin wall tube whose outer diameterclosely matches the inner diameter of the tubular member 10. Generally,the disposable mask can have the same length, or can be larger orsmaller than the length of the tubular member, depending, of course, onthe amount of laser cutting to be performed on the tubular member 10. Asis depicted in FIG. 1, the length of the masking sleeve 16 is longerthat the length of the tubular member 10.

The method further includes the cutting of the tubular member 10 andmasking sleeve 16 by laser cutting apparatus 22, shown schematically inthe drawing figures. In one aspect of the present invention, the lasercutting apparatus 22 utilizes a pressurized inert gas, such as argon orhelium, rather than air or oxygen, to create the slots or kerfs 24extending through the wall of the tubular member 10 and masking sleeve16. In the method of the present invention, both the tubular member 10and masking sleeve 16 are cut simultaneously by the laser cuttingapparatus 22. Generally, as is schematically depicted in FIG. 3, a laserbeam 26 locally heats the tubular member 10 and masking sleeve 16 whilethe pressurized inert gas, depicted by arrow 28, is blown through asmall coaxial orifice 30 directly onto the heated region in order tocreate the slots or kerfs 24.

Laser cutting of the tubular member 10 and masking sleeve 16 generallybegins by focusing a laser beam on a targeted spot on the tubing. Thespot is melted by the laser beam while the pressurized inert gas forcesthe molten material through the walls of the tubular member and maskingsleeve 16 to form the kerf 24. The tubular member 10 and sleeve 16 aremoved by an automated mechanism of the laser cutting apparatus to createthe desired pattern. Once the laser beam burns through the side wall ofthe tubular member 10 and masking sleeve 16, the laser beam couldpossibly continue to strike the opposite inside surface of the tubularmember. However, the masking sleeve 16 covers the inner surface of thetubular member 10, thus preventing any damage to the tubular member. Inthe laser cutting process, recast material 32 which is forced throughthe kerf via the pressurized inert gas is collected as a disposable masson the masking sleeve 16, rather than being “welded” to the innersurface 14 of the tubular member 10. In this aspect of the invention,the masking sleeve 16 forms a protective barrier for the inner surface14 of the tubular member 10. FIG. 2 shows how the recast material wouldstrike and damage the inner surface of the tubular member 10 if adisposable mask is not present. Also, since the inert gas preventssidewall oxidation, the method of the present invention allows the cutwork piece to be processed downstream without the need for substantialautomated or manual grit blasting prior to electropolishing.

As is best depicted in FIG. 4, the laser cutting process not onlyresults in the formation of recast material 32 disposed as bulk waste onthe inner surface 20 of the masking sleeve 16, but also results in theformation of recast droplets 34 near the lower portion of the kerf 24.These recast droplets 34 cause portions of the tubular member 10 andmasking sleeve 16 to somewhat bond together, forming an unwanted meldedstructure which must be removed from the tubular member 10 beforeadditional processing proceeds. These recast droplets 34 are primarilysolidified droplets of the material forming the tubular member 10.

The present invention utilizes a variety of mechanical techniques toremove the sacrificial mask and dross from the tubular member, alongwith a variety of chemical removal techniques which can be coupled withthese mechanical techniques to quickly and cleanly remove the dross andsacrificial mask from the inner wall of the laser cut tubular member.

In one particular post-cutting procedure, the purely mechanicaltechniques for removing the dross and sacrificial mask is to attack thedross only, utilizing equipment which will grind, hone or bead-blast thedross only. For example, dross also can be removed utilizing a tool suchas a wire brush or reamer. Another way to clean the lased tubular memberwould be to mechanically attack the sacrificial mask only. Similarmechanical removing techniques could be used to remove the sacrificialmask. Lastly, these same techniques could be used to mechanically attackboth the dross and sacrificial mask. These various techniques providesimple but useful manufacturing steps to separate the lased tubularmember from the sacrificial mask and dross.

The process of mechanically separating the disposable mask from thetubular member can use, for example, any type of device which will breakthe recast droplets and the contact between the surfaces of the tubularmember and disposable mask. For example, the mechanical process ofremoving the sacrificial material from the tubular member can beperformed by inserting a mandrel (not shown) into the lumen of themasking sleeve. The mandrel can be twisted causing the disposable maskto break contact with the inner surface 14 of the tubular member 10. Thetwisting action of the mandrel helps to peel the disposable maskingmaterial from the inner surface of the tubular member and break the bondcreated by the recast material and droplets. The surface of the mandrelcould include prongs, flutes, knurling or other friction enhancingstructure which increases frictional contact between the mandrel anddisposable mask. It should be appreciated that other means formechanically removing the disposable mask from the tubular member can beutilized in accordance with the present invention.

Another particular mechanical technique for removing the sacrificialmask and dross from the tubular member would require the separation ofthe components by employing different material properties between thelased tubular member and the sacrificial mask. For example, the tubularmember and sacrificial mask could be made from different materialshaving different coefficients of thermal expansion. For example, heat orcoldness could be applied to the cut work piece to cause the tubularmember to either expand or contract, which should break the sacrificialmask away from the lased tubular member. Alternatively, the sacrificialmask could be made from a material which will expand or contract uponapplication of heat or coldness to cause the mask to break away from thetubular member.

In another mechanical procedure, a lased tubular member made from aself-expanding material, such as Nitinol, could be crushed and rolled toallow the tubular member to spring back to shape. The sacrificial maskcould be made from a material which is comparatively not very elastic,so that the crushing and rolling of the tubular member should break anyconnection between the sacrificial mask and the tubular member.Alternatively, the lased tubular member could be expanded, rather thanbeing rolled, which again should cause the sacrificial mask to breakaway from the tubular member.

Still other removal procedures which can be implemented in accordancewith the present invention include mechanically peeling the sacrificialmask from the lased tubular member or mechanically gripping andpulling/pushing the sacrificial mask out of the tubular member. A reameror mandrel could be used to grip the inside surface of the sacrificialmask to allow a technician to pull or push the mask from the tubularmember. Other tools could be implemented as well to accomplish this typeof mechanical removal. Additionally, removal procedures couldalternatively call for the laser cut tubular member/sacrificial mask tosubjected to vibration, which would break the sacrificial mask from thetubular member.

In another aspect of the present invention, the procedure for removingthe sacrificial mask and dross from the lased tubular member wouldutilize a combination of chemical removal techniques with mechanicalremoval techniques, such as the ones addressed above, to achieve a cleanworkpiece which is ready for electropolishing. For example, aftercutting, the lased tubular member and sacrificial mask can be subjectedto a chemical attack which would only attack the tubular member itself,i.e. the dross. A chemical solution would be applied to both the tubularmember and sacrificial mask. The application of the chemical solution isdesigned to primarily attack the tubular member, rather than thedisposable mask material. As such, the chemicals are selected whichpreferably attack the material of the tubular member, leaving thesacrificial mask material generally unharmed. In one aspect of theinvention, the chemical solution attacks the tubular member by etchingit.

The process for removing the recast material and droplets from thetubular member requires a chemical solution to be applied to both thetubular member 10 and masking sleeve 16. The chemical solution can bedirectly applied to the tubular member 10 and masking sleeve 16 or thecomponents could be dipped into a bath containing the chemical solution.The chemical solution is designed to primarily attack the tubular member10, leaving the masking sleeve unharmed. It should be noted that therecast droplets 34 have a very large surface area to volume ratio andtherefore they are much more readily attacked by the chemical solutionthan the larger body of the tubular member 10 itself. This process ofapplying a chemical solution which primarily attacks the tubular member10 eliminates or weakens much of the recast droplets 34, therebyallowing the tubular member 10 and the masking sleeve 16 to be moreeasily separated.

After the chemical solution has acted on the tubular member, the tubularmember and the sacrificial mask material can be further processed, ifneeded, using mechanically separation procedures. This mechanicalseparation causes any recast material that is still adhering to thetubular member to be broken off, leaving the inner surface of thetubular member virtually free of any recast material. After the chemicalsolution is applied to the tubular member 10 and masking sleeve 16 andthe recast material is weakened, the tubular member and the maskingsleeve 16 should be relatively easy to separate using mechanicaltechniques. Since the masking sleeve is virtually unharmed by thechemical solution, it remains stiff and capable of breaking the recastmaterial formed at the kerfs when twisted away from the tubular member.Any recast material or droplets 34 that still adhere to the tubularmember 10 will be broken off, leaving the inner surface 14 of thetubular member 10 virtually free of any recast material.

The removal of the sacrificial material from the inner surface of thetubular member can be performed mechanically, for example, by deviceswhich will break the recast material formed in the kerfs and elsewhere.The mechanical process of removing the sacrificial material from thetubular member can be performed, for example, by inserting a mandrelinto the inner lumen of the disposable mask and twisting the sacrificialmask from the inner surface of the tubular member. Any of the mechanicaltechniques mentioned above could be implemented to remove thesacrificial mask and any remaining dross from the tubular member, afterthe chemical application has been completed.

In another aspect of the present invention, the process of removing themask and dross from the tubular member would encompass the applicationof a chemical solution which attacks only the sacrificial mask, leavingthe tubular member virtually unharmed. The chemical attack can eitherdissolve the sacrificial mask completely, or could just weaken thesacrificial mask. Any one of a number of mechanical procedures couldthen be implemented to remove any remaining portions of the sacrificialmask and dross.

The removal process could encompass the application of chemicals whichattacks both the sacrificial mask and tubular member. In this process, achemical solution could first be applied which attacks or dissolves onlythe dross. Thereafter, a second chemical solution could be applied whichattacks only the sacrificial mask. Alternatively, the chemical solutionwhich only attacks the sacrificial mask could be applied first and laterthe chemical solution which attacks the dross could be applied. In yetanother removal procedure, a chemical solution which simultaneouslyattacks both the tubular member and sacrificial mask could be applied.In one scenario, the chemical solution could completely dissolve thesacrificial mask and dross, eliminating the need for any furthermechanical separation. Alternatively, if the chemical solution onlyweakens the dross and sacrificial mask, any remaining dross and maskmaterial could be mechanically removed using any of the mechanicaltechniques mentioned above.

The use of the present method in forming a medical device, such as astent, reduces the amount of grit blasting or chemical removal due tothe lack of oxidized cast material since air or oxygen is no longer usedin the laser cutting process. Again, the use of the inert gas eliminatesthe possibility that the sidewalls or the recast material will beoxidized during the laser cutting step. As a result, the elimination ofsidewall oxidation helps to prevent cracking or fracturing of the stentduring use and reduce or even eliminates some of the subsequentprocessing which would be otherwise utilized in order to remove theoxidized material from the tubular member. As a result, the formed stentcan be sent for electropolishing without the need for additionalprocessing, or with only a minimal amount of mechanical processing,which reduces the chance of breaking or irreparably damaging the oftenfragile struts forming the stent.

Although the sacrificial mask is disclosed herein as a disposablemasking sleeve, it should be appreciated that other forms andconfigurations of a disposable sacrificial mask could be used inaccordance with the present invention. For example, the mask may becomprised of a flat foil that is rolled into a cylinder and theninserted into the tubular member. Additionally, the disposable maskcould be produced through the build-up of material on the inner surfaceof the tubular member by such methods as electroplating, plasmaspraying, physical vapor deposition, chemical vapor deposition and thelike. However, it is important that the disposable sacrificial maskmaterial does not become metallurgically bonded or otherwise so stronglyaffixed to the tubular member that the two components cannot be easilyseparated from each other after laser cutting and the application of themechanical and/or chemical processing of the cut workpiece. Thus, thedisposable mask and the tubular member should preferably be made fromdissimilar materials that do not easily weld or bond to one another. Inone particular method of the present invention, steel or stainless steelcan be used to form the disposable mask when a Nitinol tubular member isbeing fabricated because of their inherent metallurgicalincompatibility. For example, the disposable mask could be formed fromany material capable of withstanding the temperatures of the expelledmolten material, such as ceramics, metals, composites, or hightemperature polymers. Other suitable metals include steel, copper,magnesium, nickel, cobalt, molybdenum, tantalum, niobium, titanium,zirconium, tin, iron, or any other alloy based on these metals.

The pressurized inert gas used with the laser cutting apparatus includeargon or helium as these two inert gases are economical and commerciallyavailable. However, it should be understood that the laser cuttingapparatus could utilize any inert gas to prevent the work piece fromoxidizing. Since argon and helium gases are more readily availablecommercially, these inert gases may serve to be more economical from acost standpoint.

One particular method of chemically attacking the tubular member resultsin the material forming a tubular member to be etched away to weaken anyrecast material remaining on the workpiece. In this particular method ofthe present invention, a nickel-titanium or a ternary nickel-titaniumalloy is the material used to form the tubular member and stainlesssteel is used to form the disposable mask. The tubular member and maskcan be immersed in a solution of approximately 3% hydrofluoric acid (HF)and 50% nitric acid to chemically etch the recast material formed by thetubular member to help break the strength of the bond created by therecast material. The acid can rapidly etch away at the nickel-titaniumalloy while the stainless steel disposable mask remains relativelyundamaged. In this aspect of the invention, the acid will leave thestainless steel material relatively unharmed. The submersion of thesetwo components in the hydrofluoric acid can be for a time duration fromapproximately 30-45 seconds, after which the components are removed. Ifneeded, the mechanical process of removing the disposable mask from thetubular member can then be performed. In another variation, a steelsleeve could be used and the aforementioned HF-nitric solution could beused to simultaneously and completely dissolve both the steel sleeve andnitinol dross in only 10-seconds. This embodiment is particularly usefulwhen the workpiece is particularly long or delicate therefore making themechanical removal of the sleeve difficult. It should be appreciatedthat other chemical solutions could be utilized in accordance with thepresent invention. For example, the chemical solution can be acidic,alkaline, or any other chemically reactive agent which preferablyattacks the tubular member rather than the disposable mask material orsimultaneously attacks both. The strength of the chemical solution andthe time duration that the chemical solution remains on the componentswill depend, of course, on the type of materials used for the tubularmember and disposable mask and the type of chemical utilized.

While the invention has been illustrated and described herein, in termsof methods for fabricating a medical device, such as an intravascularstent, it will be apparent to those skilled in the art that the methodscan be used with other devices. Further, other modifications andimprovements can be made without departing from the scope of the presentinvention.

1. A method for making a device, the method comprising: providing atubular member with an inner lumen which will be formed into the device;masking at least a portion of the surface of the lumen of the tubularmember with a removable sacrificial material; selectively removing aportion of the tubular member and sacrificial material using a laserdevice; and mechanically removing the sacrificial material from thesurface of the lumen of the tubular member.
 2. The method of claim 1,wherein the laser device uses a pressurized inert gas to remove theportion of the tubular member and sacrificial material.
 3. The method ofclaim 2, wherein the inert gas is argon.
 4. The method of claim 1,wherein the sacrificial material is a tubular sleeve upon which thetubular member is mounted.
 5. The method of claim 1, wherein thesacrificial material is stainless steel.
 6. The method of claim 1,further including: applying a chemical solution to the tubular memberand sacrificial material which primarily attacks the tubular member. 7.The method of claim 7, wherein the chemical solution primarily attacksthe tubular member by etching the tubular member.
 8. The method of claim6, wherein the chemical solution is applied for a sufficient time toprimarily attack the tubular member but not the sacrificial material. 9.The method of claim 6, wherein the chemical solution is hydrofluoric andnitric acid.
 10. The method of claim 1, wherein the sacrificial materialis selected from a group of materials consisting of stainless steel,steel, copper, magnesium, nickel, cobalt, molybdenum, tantalum, niobium,titanium, zirconium, tin, iron, or any other alloy based on thesemetals.
 11. The method of claim 1, wherein the tubular member is madefrom binary nickel-titanium.
 12. The method of claim 7, wherein thechemical solution is selected from a group consisting of acids,alkalines and any chemically reactive agent.
 13. The method of claim 1,further including: applying a chemical solution to the tubular memberand sacrificial material for a time duration in which primarily attacksthe sacrificial material.
 14. The method of claim 1, further including:applying a chemical solution to the tubular member and sacrificialmaterial for a time duration in which the chemical solution primarilyattacks both the sacrificial material and tubular member.
 15. The methodof claim 6, further including: applying a second chemical solution tothe tubular member and sacrificial material for a time duration in whichthe second chemical solution primarily attacks the sacrificial material.16. The method of claim 1, wherein the mechanical removal of thesacrificial material from the surface of the lumen of the tubular membercomprises: inserting an instrument into the lumen of the tubular memberto frictionally engage the sacrificial material; and manipulating theinstrument to remove the sacrificial material from the tubular member.17. The method of claim 1, wherein the tubular member is made from anickel-titanium alloy and the mechanical removal of the sacrificialmaterial from the surface of the lumen of the tubular member comprises:applying an inward or outward force on the tubular member to break anybonding between the tubular member and sacrificial material.
 18. Themethod of claim 1, wherein the tubular member is made from a materialhaving a different coefficient of thermal expansion than the sacrificialmaterial and the mechanical removal of the sacrificial material from thesurface of the lumen of the tubular member comprises: applying heat orcold to the tubular member and sacrificial material to break any bondingbetween the tubular member and sacrificial material.
 19. The method ofclaim 1, wherein the mechanical removal of the sacrificial material fromthe surface of the lumen of the tubular member comprises: applyingvibration to the tubular member and sacrificial material to break anybonding between the tubular member and sacrificial material
 20. A methodfor making a laser cut device, the method comprising: providing atubular member with an inner lumen which will be formed into the lasercut device; mounting the tubular member onto a sleeve formed from aremovable sacrificial material; laser cutting a pattern into the wall ofthe tubular member and sacrificial sleeve; and applying a chemicalsolution to the tubular member and sleeve of sacrificial material for atime duration in which the chemical solution primarily attacks eitherthe tubular member or sacrificial material.
 21. The method of claim 20,wherein the laser device uses a pressurized inert gas to laser cut thetubular member and sleeve of sacrificial material.
 22. The method ofclaim 21, wherein the inert gas is argon.
 23. The method of claim 20,wherein the tubular member is made from a nickel-titanium alloy.
 24. Themethod of claim 20, wherein the sleeve of sacrificial material isstainless steel.
 25. The method of claim 20, wherein the chemicalsolution primarily attacks the tubular member by etching the tubularmember. The method of claim 20, wherein mechanically removing the sleevefrom the tubular member.
 26. The method of claim 20, further including:mechanically removing the sleeve from the tubular member.
 27. The methodof claim 26, wherein the mechanical removal of the sleeve from thetubular member comprises: inserting an instrument into the lumen of thetubular member to frictionally engage the sleeve; and manipulating theinstrument to remove the sleeve of sacrificial material from the tubularmember.
 28. The method of claim 26, wherein the tubular member is madefrom a nickel-titanium alloy and the mechanical removal of the sleeve ofsacrificial material from the tubular member comprises: applying aninward or outward force on the tubular member to break any bondingbetween the tubular member and sleeve.
 29. The method of claim 26,wherein the tubular member is made from a material having a differentcoefficient of thermal expansion than the sleeve of sacrificial materialand the mechanical removal of the sleeve from the tubular membercomprises: applying heat or cold to the tubular member and sleeve tobreak any bonding between the tubular member and sleeve.
 30. The methodof claim 26, wherein the mechanical removal of the sleeve from thetubular member comprises: applying vibration to the tubular member andsleeve to break any bonding between the tubular member and sleeve.